HAMMETT RHO(+) VALUES AS KINETIC EVIDENCE FOR THE CONCERTED BIOMIMETIC BICYCLIZATION MECHANISM

Chlorides 1 (1-aryl-1-chloro-5,9-dimethyl-5,9-undecadienes) with vario us phenyl substituents were prepared (Y = p-OCH3, p-CH3, H, p-Br, and m-Br), and solvolysis rates were measured in 80% (v/v) aqueous ethanol and in 97% (wt/wt) aqueous 2,2,2-trifluoroethanol. The Hammett rho(+) values obtained are -1.5 and -1.8, respectively, indicating the conce rted bicyclization. Comparison with rho(+) values that correspond to s olvolysis of the benzylic squalene derivatives 3 (rho(+) = -1.8 and -1 .6 in the same solvents) leads to the conclusion of the concerted bicy clization in 3 and may also suggest concerted bicyclization under biom imetic conditions in the natural precursor, 2,3-epoxysqualene, as well .